Number Representation in Perceptual Decisions

Abstract

An interesting unsolved case in cognitive science, and one that impacts education and decision-making, is the whole number bias: when people compare fractions they rely on the numerical values of the components (numerator or denominator). A handful of theories have been proposed to explain the bias in Arabic formats, all sharing the assumption of some fundamental difficulty in estimating ratio magnitudes. This thesis contrasts them in a perceptual setting by means of a cognitive model of ratio comparisons. Contrary to the assumption, for the visual system the bias is automatic even when fraction magnitudes are mentally available (Chapter 2a). Moreover, it is present in indigenous populations living in the Amazon, suggesting a limited role of culture and a more generic feature of cognition (Chapter 2b). The automatic activation of numerical magnitude can impact confidence (Chapter 2c), visual selection (Chapter 3) and modulate how the motor system displaces effectors (Chapter 4). The overall results are consistent with the view that the whole number bias is part of a larger phenomenon: people spontaneously and robustly represent numerical value across a variety of perceptual decision tasks.